Chemical sensitization of photographic emulsions



Patented July 22, 1952 CHEMICAL SENSITIZATION OF PHOTO- GRAPHICEMULSIONS' Wesley G; Lowe and Jean E. Jones, Rochester, N. Y., assignorsto Eastman Kodak Company, Rochester, N. Y., a corporation of New JerseyNo Drawing. Application November 18, 1948,

Serial No, 60,816 a 11- Claims. (01. 95-7) This invention relates tophotographic emu1 sions and more particularly to chemical sensitizerstherefor.

It is Well known that silver halide emulsions may be chemicallysensitized with a variety of materials so as to increase the speed andgenerally the gamma of the emulsion as opposed to :optical sensitizationin which the optical 'range of sensitivity is increased' Depending uponthe materials and methods employed; it is generally regarded thatchemical sensitization results in either the formation of silver sulfideon the surface of the silver halide crystal thus increasing sensitivityor the formation of small amounts of silver from the reduction of silverhalide. The

present invention is concerned'with chemical sensitization apparently ofthe latter type.

We have discovered that when photographic silver halide emulsions arechemically sensitized with water-soluble salts furnishing-thesulfoxalate ion, appreciable increases-inlight sensitivity are obtained.Therefore, one-object ofour invention is to provide novelchemicallysensitized emulsions. Another objectis' to provide silverhalide emulsions containing sulfoxalate sensitizing as well assensitivity due to otherchefnical and optical sensitizers. Other objectswill appear from the following description of'o'ur-invention. j "j I Theobjects of our invention areyaccomplished by incorporating intophotographic emulsions a water-soluble formaldehyde sulfoxalate saltsuch as an alkali metalformaldehydevsulfoxalateparticularly sodiumformaldehyde sulfoxalate. The novel sensitizers are incorporated in' theemulsions at any stage in their preparation but'pr-eferably beforedigestion is complete. Generally in order to obtain the optimumsensitizingefiect we heat the emulsion after addition of the sulfoxalatesensitizer. The sensitizers may be used in conjunction with othercheinical-a'ndoptical sensitizers such as the Well known sulfursensitizing c'ompoundsy'for example, those disclosed in Sheppard U. S.Patents"1,574,'94l granted March 2, 1926, and 1523,499, granted April 5,1927, and may be employed before, after or'simultaneously with suchsulfur sensitizing and in conjunction with sensitizing dyes. Als o ourlnovel sensitizers areuseful with a variety of emulsions producingpronounced speed increases in either negative orpositive typ'e's ofemulsions;

a Our invention Will now be illustrated byrefer- .ence to the followingspecific examples-t Example 1' l I cc. of a promo-iodide positive typeof emulsion containing silver halide iobta n drfr grams of silvernitrate and peptized with a gelatin derivative by the process disclosed.in the pending Lowe et a1. SLapplicat'io'n Serial No.

768,478 filed August 13,1947, was adjusted to'a pH of 4.5 then treatedat F. with3iQ mg, of sodium formaldehyde sulfoxalalte; and heatingcontinued at this temperature for 20 minutes.

Following this, the emulsion was cooled to 100 F. and the pH raised to6.0 with sodium hydroxide solution. To samples of the resultant emulsionwas added hydrophilicf colloid material such as gelatin or polyvinylalcohol; respectively, and after addition .of the usual emulsionaddenda, the emulsions were coated andfdried in the usual manner. Afterexposure in an Eastman TXDeiZB Sensitometer (J. Soc. Mot. Pict. Eng.'1??- (1931) p. 536) and processing in a developer solution of thefollowing composition for six minutes, the emulsions were found tohave'materially increased in speed, as shown in the table following(samples B and F compared to samples A and Developer Sodium carbonate(dry), do' 19.0

' Potassium bromide do 0.9 Citric acid do- 0.7

Example 2' 100 cc. of the same type of emulsion as'was used in Example 1but which hadpreviously. been sensitized with arsulfur type ofsensitizer e. g. allyl thiourea, .asdescribed in the Lowe et al. in-

vention, was adjusted to pH 4.5 by dilute acetic acid and treated withsodium formaldehyde sulfoxalate as in Example 1 and samples combinedwith gelatin and polyvinyl alcohol, respectively, to obtain emulsionsthe sensitivities of which are distinctly higher than obtained by "usingeither .sensitizer separately as is shown in the table following(samples D and'H compared to samplesB. C;FandG).r

Example 3 100 cc. of emulsion prepared as described in Example 2(sensitized with: sulfur and sulfoxalate sens'itizersl were precipitatedwithidilute sulfuric acid and washedtwice with'distilled water. Afterrepeptizing the grains, the pH was adjusted to 6.0, the emulsion heatedto 120 F. and 1.0 mg. of potassium auric chloride Was added. After fiveminutes the temperature was lowered to 100 F., the emulsion was added togelatin and coated and dried as usual. Thecharacteristics of thisemulsion having combined sulfur, sulfoxalate and gold sensitizing, areshown in the table (sample K compared to samples I, J and L).

4 tion is to be taken as limited only by the scope of the appendedclaims.

What we claim is: 1. A light-sensitive photographic emulsion comprisingsilver halide and from about 0.03 to 0.75 gram per kilogram of-silvernitrate used in .making the emulsion and converted to silver halide, ofa water-soluble formaldehyde sulfoxalate salt as a sensitizing agent.

. lot/E Speed :2. ens.=- Sample Chemical sensitizer Vehicle Gamma Fog 02above I log None Gelatiin 76 02 .39 Sulioxalate 1 d 1. 58 02 80 72 .0235 1. l3 02 45 2. 52 03 3. 55 2. 51 05 4. 70 Sulfur type 2. 6 02 4. 3Sulfur and Sulfoxalate 3. 1 07 7. 3 Sulfur and Sulioxalate and Gold.--3. 2 .09 14.0 Sulfur and Gold 3. 5 04 6. 5

It is apparent from the above data that the new sulfoxalate sensitizerused in conjunction with a sulphur sensitizer has effected a speedincrease greater than that expected from the activity of the individualsensitizers when used alone. However, the speed increases obtained inabsence of sulfur sensitizing are appreciable and valuable.

In the manner of the above examples, other types of silver halideemulsions may be treated with our novel sensitizers alone or inconjunction with other chemical or optical sensitizers. The amount ofthe sulfoxalate sensitizer incorporated into an emulsion may, dependingupon the type of emulsion used, vary somewhat from the optimum amountemployed in the above examples, one-fifth to five times as muchsensitizer producing emulsion of useful sensitivity that is, from about0.03 to 0.75 gram of the sensitizer per kilogram of silver nitrate usedin making the emulsion and converted to silver halide. Less V heating isusually required when the larger amounts are employed and conversely,when using the smaller quantities of sensitizer.

The novel sensitizers may, in general, be employed i emulsionscontaining hydrophilic colloid vehicles; for example, gelatin, polyvinylalcohol, partially hydrolized cellulose esters and co-polymers ofpolyvinyl alcohol. The ratio of colloid to silver halide present duringdigestion is not critical in this type of sensitizing since thedigestion conditions can be readily adjusted as is well known in the artof sulfur sensitizing. The sensitizers are suitable for the well knowntypes of silver chloride, silver bromide and silver iodide emulsions andemulsions containing mixtures of these halides. Also the emulsions maycontain the usual addenda including antifoggants, spreading agents,coupler compounds, etc. Such emulsions are adaptable to use informingsingle as well as multi-layer films useful in color photography whichcustomarily include two or more emulsion layers on a support sensitizedto different regions of the visible spectrum and may or may not containcoupler compounds. According to our invention such color films carry atleast one emulsion layer containing a sulfoxalate salt sensitizingagent.

Our invention having been described, we would have it understood thatthe preceding description is by way of example'only and that our inven-2. A light-sensitive photographic emulsion comprising silver halide andfrom about 0.03 to 0.75 gram per kilogram of silver nitrate used inmaking the emulsion and converted to silver halide, of sodiumformaldehyde sulfoxalate as a sensitizing agent.

3. A light-sensitive photographic emulsion comprising sulfur sensitizedsilver halide and from about 0.03 to 0.75 gram per kilogram of silvernitrate used in making the emulsion and converted to silver halide, ofsodium formaldehyde sulfoxalate as an additional sensitizing agent.

4. A light-sensitive photographic emulsion comprising silver halidesensitized with a sulfur sensitizing compound, a gold salt sensitizerand sodium formaldehyde sulfoxalate.

5. A light-sensitive photographic emulsion comprising silver halideuniformly dispersed in a hydrophilic colloid vehicle and sensitized withfrom about 0.03 to 0.75 gram per kilogram of silver nitrate used inmaking the emulsion and converted to silver halide, of a water-solubleformaldehyde sulfoxalate salt.

6. A light-sensitive photographic emulsion comprising silver halideuniformly dispersed in gelatin and sensitized with from about 0.03 to0.75 gram per kilogram of silver nitrate used in making the emulsion andconverted to silver halide, of sodium formaldehyde sulfoxalate.

7. A light-sensitive photographic emulsion comprising silver halideuniformly dispersed in polyvinyl alcohol and sensitized with from about0.03 to 0.75 gram per kilogram of silver nitrate used in making theemulsion and converted to silver halide, of sodium formaldehydesulfoxalate.

8. The method of increasing the speed of a photographic silver halideemulsion which comprises imparting sulfur sensitivity to said emulsion,adjusting the pH of said emulsion to below neutrality, and effecting afurther increase in sensitivity by digesting said emulsion in thepresence of a water-soluble formaldehyde sulfoxalate salt.

9. The method of increasing the speed of a photographic silver halideemulsion which comprises imparting sulfur, sensitivity to said emulsion,adjusting the pH of said emulsion to below neutrality and effecting afurther increase in 6 REFERENCES CITED The following references are ofrecord in th file of this patent: I

Number Number UNITED STATES PATENTS Name Date Miller June 10, 1930Sheppard et a1. Nov. 3, 1936 FOREIGN PATENTS Country Date Great BritainNov. 21, 1938

1. A LIGHT-SENSITIVE PHOTOGRAPHIC EMULSION COMPRISING SILVER HALIDE ANDFROM ABOUT 0.03 TO 0.75 GRAM PER KILOGRAM OF SILVER NITRATE USED INMAKING THE EMULSION AND CONVERTED TO SILVER HALIDE, OF A WATER-SOLUBLEFORMALDEHYDE SULFOXALATE SALT AS A SENSITIZING AGENT.